Crystal oscillator with amplifier
Here we present the crystal oscillator with the amplifier on two transistors operating in a nonstandard mode. Their top nameplate frequency is 3 MHz, however, these good transistors generate and amplify the signal at frequency up to 27 MHz (what was tested). The amplifier has a pretty powerful output, which can connect any nizkoomnyj load, and the output is protected against short circuit, even long-term. The scheme can be controlled by the external generator and the result is very reliable as load and supply voltage, which has a very wide range: from 9 to 25 volts.
Figure (1) schematic diagram of such a generator. From the perspective of circuit design there is nothing unusual: the first transistor VT1 is assembled according to the scheme capacitive treatacne and allows the generation of a sinusoidal signal, whose frequency is stabilized by quartz resonator ZQ1. The second transistor VT2 is enabled by an emitter follower and amplifies the current signal from the first amplifier stage. The output connects any nizkoomnyj load, in this case, the coil L1, the secondary winding which is completely enclosed. This incorporation of coil is sometimes necessary to create a second (scalar) magnetic field.
The novelty of the scheme consists of the application of transistors, actually consisting of two components, the Darlington circuit . We are talking about the item TIP41C. Figure (1) on the right shows the an internal circuit. Used transistors work in an unusual mode that ensures a pretty fast response time and high frequency switching. If the scheme is not to collect on the composite transistors, it will not give the required characteristics or even just won't work.
Interestingly, the circuitry of the generator-amplifier you can change what the figures (2,3). In figure 2, instead of the coil on the output is set with the resistor R3, the ends of which are connected to a coaxial cable with wave resistance of 75 Ohm, and through it — to any remote loads.
The circuitry of the generator is built in such a way that it is possible control via external pulses, the amplitude should be equal to the supply voltage. This option of external control as shown in figure (2) to the right. Since the input resistance of the circuit will always be a few kilo Ohm, the external oscillator can be low-power.
The advantage of the scheme (Fig. 1,2) is the common collector of the two transistors, and therefore, if necessary at high supply voltages, these collectors can be put on a common heatsink without insulating pads. What can be said about the following scheme (Fig. 3), where collectors posted. But the inclusion of such loads in the form of a coil L1 allows you to output high-voltage unipolar pulses. Moreover, their amplitude can exceed the nameplate maximum value of the collector-emitter several times, which also shows the irregularity of the inclusion of transistors.
The duration of these pulses is determined by the inductance of the output coil. Experiments have shown that the best generator receives placie coil , but may work with a classic single layer. In the latter case, the wire winding should be dostatono thick in cross section (0.9-2mm) and have 25-50 turns. Also, the coil should not have a ferromagnetic core.
Below are the waveforms on the oscillator output to two different coils (scheme 3). Probe 1:10. The first flat coil, a wound wire of 1 mm with 35 coils. Oscillograms of the output in this case are shown in figures (4,5). The second coil is flat, having 45 turns of wire of 1 mm, wound on a frame of 30 mm. oscillograms of the output from this coil are shown in figures (6,7).
Fig.4. A flat coil. One pulse
Fig.5. A flat coil. Several pulses
Fig.6. Single-layer coil. One pulse
Fig.7. Single-layer coil. Several pulses
It should be noted that the optimal voltage power supply — 12 V. At this voltage the resistors R2 and R3 in all diagrams should be powerful enough: R2 is not less than one watt, R3 is not less than two. But if the supply voltage is above 12 V, the capacity needs to increase, and the transistors VT1 and VT2 install on the radiator.